Zinc dialkyldithiophosphate (ZDDP) has been used as an additive in formulated lubricants for many decades. The primary function of ZDDP is to provide antiwear protection to moving engine parts by interacting with iron oxides to form a protective layer.
The current understanding of the formation of antiwear films from ZDDP involves tribochemical and thermooxidative components. As ZDDP decomposes, metathiophosphates and colloidal polyphosphates are formed. The decomposition of these materials leads to the formation of low molecular weight volatile phosphorus compounds. This occurs because ZDDP is not ash-free and contains phosphorus. These decomposition compounds may have several detrimental effects on engine performance such as reduced wear protection and poisoning of the catalytic converter and/or the exhaust gas oxygen sensor.
Despite the advances in lubricant oil formulation technology, there remains a need for lubricant oil additives that provide superior wear protection and environmentally beneficial properties such as reduced exhaust emissions.
The present invention provides a synergistic combination of a premixed composition comprising a ZDDP and at least one additive that results in the formation of transient intermediates that provide superior wear protection and reduced additive volatility.